Recently, a high-speed cellular radio communication scheme called Long Term Evolution (LTE) is being practically implemented. The LTE scheme is categorized into the FD-LTE scheme and the TD-LTE scheme, on the basis of differences in the duplex scheme. The FD-LTE scheme adopts frequency-division duplex (FDD) as the duplexing scheme, with the uplink and the downlink being operated on mutually different frequency bands. The TD-LTE scheme adopts time-division duplex (TDD) as the duplexing scheme, with the uplink and the downlink being operated on the same frequency band. Both the FD-LTE scheme and the TD-LTE scheme use a frame format in which one radio frame (having a duration of 10 ms) is made up of 10 subframes each having a duration of 1 ms. In the FD-LTE scheme, the link direction does not change over time on the same frequency band, whereas in the TD-LTE scheme, the link direction may change per subframe.
In the TD-LTE scheme, a set of link directions per subframe for each radio frame (that is, a combination of the link directions of 10 subframes) is designated the link direction configuration (or the UL-DL configuration). According to Non-Patent Literature 1, seven types of link direction configurations from Configuration 0 to Configuration 6 are defined. A radio base station (designated eNB in the LTE scheme) signals to a terminal device (designated UE in the LTE scheme) by broadcasting the link direction configuration configured for each radio frame in a system information block type 1 (SIB1). In the current standard specification, the update cycle of the link direction configuration conducted using the SIB1 is 640 ms. Non-Patent Literature 2 proposes shortening this cycle to 320 ms.
In the case of updating the link direction configuration on a short cycle, a problem arises in that link direction collisions frequently occur between the two link direction configurations pre-update and post-update, as described in Non-Patent Literature 3. Link direction collisions cause loss in data transmission and control signaling at the timings when a collision occurs, lowering communication throughput. Non-Patent Literature 3 describes two cases in which link direction collisions may invite lowered throughput: the case of an acknowledgement (ACK) and a negative acknowledgement (NACK) of a downlink transmission, and the case of an uplink grant (UL grant) preceding an uplink transmission. As a solution to this problem, Non-Patent Literature 3 proposes a technique that dynamically modifies the ACK/NACK or uplink grant timing in the case of determining that a link direction collision has occurred.